By Rebecca Smith and Katherine Blunt

In a remote, wooded canyon east of Salem, Ore., a lightning-sparked fire that had been smoldering since mid-August suddenly roared to life Sept. 7. Fanned by fierce, dry winds, the Beachie Creek fire exploded from about 450 acres to more than 132,000 acres within two days.

The massive conflagration, which has since grown to more than 190,000 acres and has destroyed hundreds of homes, was made larger by downed power lines that ignited more than a dozen fires along the Santiam Canyon, public safety officials say.

Fire investigators haven't yet determined which utilities operate those lines, but some appear to be owned by Pacific Power, a unit of Berkshire Hathaway Inc.'s PacifiCorp. Pacific Power declined to comment on the fires.

Oregon's worst wildfire season in recent memory is demonstrating that the risk of fires sparked by utility equipment during hot, dry winds is no longer confined to California, as drought and climate change kill trees and alter weather patterns.

Oregon and other Western states have only recently begun grappling with the threat of massive utility-caused wildfires. Some are now experimenting with pre-emptive power shut-offs, meant to reduce the risk of power lines sparking wildfires when wind speeds pick up, and other mitigation measures pioneered by utilities in California.

In Oregon, regulated utilities last year started strengthening their plans to address wildfire risks and proposed strategies to proactively turn off power lines when threatened by strong, dry winds. Last month, the Oregon Public Utility Commission began to assess the plans as part of a recent state directive.

"The historic fire events impacting most of western Oregon have emphasized the growing wildfire risks caused by climate change, and will undoubtedly accelerate our work with the regulated utilities," the PUC said in a statement.

Firefighters assigned to the Beachie Creek fire got a close look at what happens when an energized power line tumbles down. As winds picked up on Sept. 7, a tree hit an electric line, causing power to arc into a metal fence and igniting vegetation around a wildfire command center in the town of Gates.

The flash fire quickly engulfed two buildings and destroyed equipment as the firefighters attempted to contain it. Cornered on three sides by flames, they were forced to abandon the post.

"We stayed as long as we possibly could," said Randall Rishe, a wildland firefighter who helped battle the blaze. "None of us could remember a fire progressing as quickly as what we had seen," he said.

Sgt. Jeremy Landers of the Marion County Sheriff's Office said his agency had "numerous accounts of power lines down and arcing from those lines" along State Highway 22 in Santiam Canyon, a popular recreational area. He said an investigation would have to wait until the fire is under control. As of Wednesday, it was only 20% contained.

Two other utilities with lines in the path of the Beachie Creek fire or the nearby Riverside and Lionshead fires, which have consumed more than 300,000 acres of forest and grassland, said they have no information suggesting that any of their equipment caused ignitions.

Consumers Power Inc., a small electric cooperative with 25,000 customers spread across six counties, said it disabled some equipment as a precaution to prevent accidental ignitions if tree limbs hit wires. James Ramseyer, a spokesman for Consumers Power, said he expects "there will be a full investigation and we will fully cooperate. I don't want to speculate about what it will find."

Federal investigators are also looking into the cause of the Holiday Farm fire, which has grown to 170,000 acres and has scorched the Willamette National Forest. There were several reports of fallen power lines in the fire zone, though whose they are is unclear.

The Eugene Water and Electric Board, a city-owned utility that serves 200,000 people, operates transmission lines that take electricity from powerhouses on the McKenzie River to the Eugene area. Joe Harwood, a spokesman for the utility, said it shut off power to thousands of customers in the McKenzie River Valley on Sept. 7, trying to prevent fires from starting. He said the utility has formed a "formal response team so that we can provide relevant facts to the investigators."

Other utilities also have facilities nearby including the federally-owned Bonneville Power Administration. A Bonneville spokesman said it had no information linking its equipment to fires.

Wildfires pose acute financial risk for utilities in California, where a legal standard known as "inverse condemnation" renders them liable for property damage caused by their equipment, even if they aren't found negligent in maintaining it.

PG&E Corp., California's largest utility, faced billions of dollars in liability costs and filed for chapter 11 bankruptcy protection after its equipment sparked more than a dozen destructive wildfires in 2017 and 2018. It emerged from bankruptcy this summer after reaching settlement deals with fire victims, insurers and other claimants for more than $25 billion.

In Oregon and other Western states, utilities are liable for property damage and other losses if their equipment sparks fires, but only if they're found negligent. In the Pacific Northwest, many residents are served by small customer-owned utilities, in addition to larger ones owned by investors.

Some of those utilities have lately grappled with fire-related financial risk. In August 2015, tree branches brushed against a distribution line owned by the Okanogan County Electric Cooperative in north-central Washington. Sparks from the line ignited the 11,200-acre Twisp River Fire that killed three firefighters. Federal prosecutors in Washington brought claims against the utility, saying its tree-trimming program was poorly designed. The utility settled the claims for $1.1 million.

James McCormick, an attorney with law firm Evergreen Personal Injury Counsel in Tacoma, Wash., sued the cooperative on behalf of a severely injured firefighter. He said he anticipates more utilities in the region will be forced to re-evaluate their operations, and the condition of their power lines, as wildfire risks become more severe.

"It's going to be on the utility to make a more concerted effort," he said. "There's got to be more scrutiny on maintaining these things."

Write to Rebecca Smith at rebecca.smith@wsj.com and Katherine Blunt at Katherine.Blunt@wsj.com